Horizons: Exploring the Universe (MindTap Course List)
14th Edition
ISBN: 9781305960961
Author: Michael A. Seeds, Dana Backman
Publisher: Cengage Learning
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Chapter 12, Problem 11P
To determine
The wavelength of infrared
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If the hottest star in the Carina Nebula has a surface temperature of 51,000 K, at what wavelength (in nm) does it radiate the most energy?
Hint: Use Wien's law:
?max =
2.90 ✕ 106 nm · K
T
How does that compare with 91.2 nm, the wavelength of photons with just enough energy to ionize hydrogen?
-The wavelength calculated above is shorter than 91.2 nm. Photons at this calculated wavelength will have more than enough energy to ionize hydrogen.
-The wavelength calculated above is longer than 91.2 nm. Photons at this calculated wavelength will have more than enough energy to ionize hydrogen.
-The wavelength calculated above is shorter than 91.2 nm. Photons at this calculated wavelength will not have enough energy to ionize hydrogen.
-The wavelength calculated above is longer than 91.2 nm. Photons at this calculated wavelength will not have enough energy to ionize hydrogen.
A galaxy's rotation curve is a measure of the orbital speed of stars as a function of distance
from the galaxy's centre. The fact that rotation curves are primarily flat at large galactocen-
tric distances (vrot(r) ~ constant) is the most common example of why astronomer's believe
dark matter exists. Let's work out why!
Assuming that each star in a given galaxy has a circular orbit, we know that the accelera-
tion due to gravity felt by each star is due to the mass enclosed within its orbital radius r and
equal to v?/r. Here, ve is the circular orbit velocity of the star. (a) Show that the expected
relationship between ve and r due to the stellar halo (p(r) xr-3.5) does not produce a flat
rotation curve. (b) Show that a p(r) ∞ r¯² density profile successfully produces a flat ro-
tation curve and must therefore be the general profile that dark matter follows in our galaxy.
Some interstellar Properties.
Use excel calculator to fill in the missing figures.
1 ly = 365 × 24 × 60 × 60 × 300, 000km/s = 9.46 × 10^12 km
Chapter 12 Solutions
Horizons: Exploring the Universe (MindTap Course List)
Ch. 12 - Why is it difficult to specify the dimensions of...Ch. 12 - Why didn’t astronomers before Shapley realize how...Ch. 12 - Prob. 3RQCh. 12 - Prob. 4RQCh. 12 - Prob. 5RQCh. 12 - Prob. 6RQCh. 12 - Prob. 7RQCh. 12 - Prob. 8RQCh. 12 - Prob. 9RQCh. 12 - Prob. 10RQ
Ch. 12 - Prob. 11RQCh. 12 - Prob. 12RQCh. 12 - Prob. 13RQCh. 12 - Prob. 14RQCh. 12 - Prob. 15RQCh. 12 - Prob. 16RQCh. 12 - Prob. 1DQCh. 12 - Prob. 2DQCh. 12 - Prob. 1PCh. 12 - Prob. 2PCh. 12 - Prob. 3PCh. 12 - Prob. 4PCh. 12 - Prob. 5PCh. 12 - Prob. 6PCh. 12 - Prob. 7PCh. 12 - If the Sun is 4.6 billion years old, how many...Ch. 12 - Prob. 9PCh. 12 - Prob. 10PCh. 12 - Prob. 11PCh. 12 - Prob. 12PCh. 12 - Prob. 1LTLCh. 12 - Prob. 2LTL
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- Consider the following data on four stars: Which star would have the largest radius? Which star would have the smallest radius? Which star is the most common in our area of the Galaxy? Which star is the least common?arrow_forwardThe best parallaxes obtained with Hipparcos have an accuracy of 0.001 arcsec. If you want to measure the distance to a star with an accuracy of 10%, its parallax must be 10 times larger than the typical error. How far away can you obtain a distance that is accurate to 10% with Hipparcos data? The disk of our Galaxy is 100,000 light-years in diameter. What fraction of the diameter of the Galaxy’s disk is the distance for which we can measure accurate parallaxes?arrow_forwardA molecular cloud is about 1000 times denser than the average of the interstellar medium. Let’s compare this difference in densities to something more familiar. Air has a density of about 1 kg/m3, so something 1000 times denser than air would have a density of about 1000 kg/m3. How does this compare to the typical density of water? Of granite? (You can find figures for these densities on the internet.) Is the density difference between a molecular cloud and the interstellar medium larger or smaller than the density difference between air and water or granite?arrow_forward
- Using the information provided in Table 18.1, what is the average stellar density in our part of the Galaxy? Use only the true stars (types OM) and assume a spherical distribution with radius of 26 light-years. Stars within 21 Light-Years of the Sunarrow_forwardA given star orbits the center of its galaxy at an average speed of v_star, at a distance of r_star from the center. The galaxy has 2 spiral arms, and the arms themselves orbit slower than the star -- at the same radius, they orbit at a speed of v_arm (in the same direction as the star). The galaxy's age is t_gal. In the history of this galaxy, how many times did this star cross through a spiral arm? Values: v_star = 200 km/s, r_star = 9 kpc, v_arms = 46 km/s, t_gal = 4 Gyrarrow_forwardAmong the globular clusters orbiting a distant galaxy, one is moving at 534 km/s and is located 14 kpc from the center of the galaxy. Assuming the globular cluster is located outside most of the mass of the galaxy, what is the mass of the galaxy? Convert your answer to solar masses. (Hint: Use the formula for circular velocity, Vc = GM r ; make sure you convert relevant quantities to units of meters, kilograms, and seconds. Note: 1 pc = 3.1 ✕ 1016 m.)arrow_forward
- The disk of the Milky Way galaxy contains roughly 200 billion (1 billion = 109 ) stars. The disk is not solid, but rather is a volume about 100,000 light-years in diameter (1 ly = 9500 billion kilometers) and 1000 light-years in thickness. What is the number density of stars in the Milky Way galaxy disk, in units of stars per cubic light-year? How about in units of stars per cubic km?arrow_forwardAnalyzing the spectrum of a distant galaxy, you discover evidence that a type la supernova is occurring in that galaxy. A type la supernova has a peak luminosity of about 1010 solar luminosities (1 solar luminosity = 3.8e26 Watts). Looking at an image of the galaxy, you estimate that here on earth your telescope only sees a brightness of 8.45E-10 Watts/m². Using this information and the brightness equation, how distant is the galaxy in which the supernova is occurring? Give your answer in It yrs.arrow_forwardThe difference in absolute magnitude between two objects is related to their fluxes by the flux-magnitude relation: FA / FB = 2.51(MB - MA) A distant galaxy contains a supernova with an absolute magnitude of -19. If this supernova were placed next to our Sun (M = +4.8) and you observed both of them from the same distance, how much more flux would the supernova emit than the Sun? Fsupernova / FSun = ?arrow_forward
- Suppose you want to observe the molecular gas in a galaxy with redshift z using the rotational transition of CO J=4-3. What frequency would you observe this transition at? (Hint: the CO J=1-0 emits a photon at 115.27 GHz, and higher order transitions emit photons with frequencies in multiples of J. Express your answer as an integer. Values: z = 3.7arrow_forwardSuppose that stars were born at random times over the last 1010 years. The rate of star formation is simply the number of stars divided by 1010 years. The fraction of stars with detected extrasolar planets is at least 18%. The rate of star formation can be multiplied by this fraction to find the rate planet formation. How often (in years) does a planetary system form in our galaxy? Assume the Milky Way contains 8 × 1011 stars.arrow_forward
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